Process for producing single crystal

ABSTRACT

A method of producing a single crystal according to Czochralski method comprising the steps of, charging polycrystalline material into a crucible, heating and melting the polycrystalline material by a heater disposed so as to surround the crucible, immersing a seed crystal into the material melt and then pulling the seed crystal to grow a single crystal, wherein in the case of growing a single crystal of which resistivity is controlled by doping with boron, the highest temperature of the crucible is controlled to be 1600° C. or less to grow the single crystal. Thereby, there is provided a method of producing a single crystal in which generation of dislocation is prevented when a single crystal having high gettering property and doped with boron is produced, and thus the single crystal can be produced at high productivity and at low cost.

TECHNICAL FIELD

The present invention relates to a method for producing a singlecrystal, more particularly, to a method for producing a silicon singlecrystal in which boron is doped as a dopant.

BACKGROUND ART

Czochralski method (CZ method) and Floating Zone method (FZ method) isconventionally known as a method for producing a single crystal like asilicon single crystal.

In order to produce a silicon single crystal by CZ method, an apparatus30 for producing a single crystal as shown in FIG. 4 is used.Polycrystalline silicon is charged as a raw material into a crucible 5,and the polycrystalline silicon is heated and melted by a heater 7disposed so as to surround the crucible 5. Next, after a seed crystal 14is immersed into a material melt 4, the seed crystal is gradually pulledwith being rotated to grow a single crystal 3. In recent years, a singlecrystal has a larger size, and it has become common to use so-called MCZmethod in which a single crystal 3 is grown with applying a magneticfield to the melt 4.

The grown silicon single crystal is subsequently subjected to processesof slicing, chamfering, polishing and so on to obtain a mirror-surfacewafer. Moreover, there is a case that an epitaxial layer is furtherformed on the mirror-surface wafer. In such an epitaxial wafer whenheavy metal impurities exist on a silicon wafer to be a substrate,characteristic failure of a semiconductor device arises. Thus it isnecessary to reduce heavy metal impurities as much as possible.

For that reason, significance of gettering technique has more and moreincreased as one of the techniques reducing heavy metal impurities. Ithas become common to use a P-type silicon wafer having high getteringeffect and low resistivity (e.g., 0.1 Ω·cm or less) as a substrate foran epitaxial wafer. Because an epitaxial wafer using a substrate of sucha single crystal with low resistivity is advantageous in regard toproblems of latch up and gettering, the wafer has drawn attention as awafer of high quality.

Furthermore, it has also become common that nitrogen is doped for thepurpose of increasing BMD, controlling a size of Grown-in defect and soon (for example, see Japanese Patent Laid-open (Kokai) No. 2000-44389and Japanese Patent Laid-open (Kokai) No. 2003-2786).

Therefore, in recent years, it has become common to grow by MCZ method(or CZ method) a P-type (boron-doped) silicon single crystal with lowresistivity which is doped with nitrogen in view of problem of getteringand so on, and has a diameter of 200 mm or more, particularly a largediameter of 300 mm.

In this connection, when a single crystal is grown by CZ method, itoften happens that dislocation is generated during growth and thecrystal turns into polycrystal. If dislocation is generated, slipdislocation is propagated not only to the portion that is subsequentlygrown but also to the portion that was grown before, and a singlecrystal, that is, value as a product is lost. For this reason,conventionally when dislocation is generated, the grown single crystalis melted again (remelted) and a single crystal is grown again(regrown). However, because conducting such remelting and regrowing overand over again leads to reduction of productivity, it is preferable toprevent generation of dislocation.

DISCLOSURE OF THE INVENTION

Then, the present inventors performed investigations in regard togeneration of dislocation. Consequently, it has been found that, when asingle crystal doped with boron, particularly a single crystal with lowresistivity (e.g., 0.1 Ω·cm or less) is grown, generation of dislocationfrequently occurs in comparison to a crystal with normal resistivity,the number of times of melting a single crystal in which dislocation wasgenerated and growing a crystal again is increased, and thus it leads toconsiderable decrease of productivity.

The present invention was accomplished in view of the aforementionedproblems. An object of the present invention is to provide a method ofproducing a single crystal that, when a single crystal having highgettering ability and doped with boron is produced, generation ofdislocation is inhibited and the crystal can be produced with highproductivity and at low cost.

In order to achieve the aforementioned object, according to the presentinvention, there is provided a method of producing a single crystalaccording to Czochralski method comprising the steps of, chargingpolycrystalline material into a crucible, heating and melting thepolycrystalline material by a heater disposed so as to surround thecrucible, immersing a seed crystal into the material melt and thenpulling the seed crystal to grow a single crystal, wherein in the caseof growing a single crystal of which resistivity is controlled by dopingwith boron, the highest temperature of the crucible is controlled to be1600° C. or less to grow the single crystal.

As described later, it has been found by analyses of the presentinventors that one of the causes of generating dislocation when a singlecrystal is produced by CZ method is boron nitride (BN) formed at atemperature of approximately 1500° C. or more. Then, in the case ofgrowing a single crystal of which resistivity is controlled by dopingwith boron, if the highest temperature of a crucible is controlled to be1600° C. or less to grow the single crystal, formation of boron nitrideis inhibited and generation of dislocation due to boron nitride isprevented. Therefore, productivity can be improved and a single crystalhaving high gettering ability and doped with boron can be produced atlow cost.

In this case, it is preferable that the single crystal doped with boronis grown so that the resistivity of the single crystal to be grown is0.1 Ω cm or less.

If resistivity of a single crystal to be grown is more than 0.1 Ω cm,there is a case that it might cause little problem because a dopingamount of boron is relatively small. However, because concentration ofboron is considerably high in a single crystal with low resistivity of0.1 Ω cm or less, even an existence of a little nitrogen easily leads togeneration of dislocation due to BN. Accordingly, the present inventionhas especially beneficial effect on growing such a single crystal withlow resistivity.

On the other hand, it is preferable that the single crystal doped withboron is grown so that the resistivity of the single crystal to be grownis 0.001 Ω cm or more.

In the case of growing a single crystal with a resistivity less than0.001 Ω cm, a doping amount of boron becomes extremely large, and itbecomes difficult to be crystallized as a single crystal. Accordingly,it is preferable that the single crystal doped with boron is grown sothat the resistivity of the single crystal is 0.001 Ω cm or more.

Moreover, it is preferable that the single crystal doped with nitrogenis grown so that concentration of nitrogen in the single crystal to begrown is from 1×10¹⁰/cm³ to 5×10¹⁵/cm³.

If a single crystal is grown by doping with nitrogen so thatconcentration of nitrogen is within the above-mentioned range,crystallization of single crystal isn't adversely affected, BMD andGrown-in defect are sufficiently controlled, and a single crystal havingeven higher gettering ability can be certainly produced. Furthermore, inthe case of growing a single crystal doped with both boron and nitrogen,boron nitride is very likely to be formed when concentration of nitrogenis within the above-mentioned range even if its resistivity is a highresistivity of 1000 Ω cm of which boron is doped at low concentration.However, formation of boron nitride is inhibited by controlling thehighest temperature of a crucible to be 1600° C. or less, and thus thepresent invention particularly has beneficial effect.

It is preferable that a silicon single crystal is grown as the singlecrystal.

A silicon single crystal is in high demand. A P-type silicon singlecrystal with high quality can be produced at lower cost when the presentinvention is applied to the production.

Furthermore, when the single crystal is grown, it is preferable that amagnetic field of at least 300 gauss or more is applied to the materialmelt to grow the single crystal.

In recent years, it has become common to produce a single crystal by MCZmethod. When a magnetic field is applied with an intensity of 300 gaussor more, an effect of suppressing a convection of a melt is increasedand temperature gradient tends to be generated. Therefore, temperatureof the melt tends to be high. However, if a single crystal is grown withcontrolling the highest temperature of a crucible to be 1600° C. orless, the temperature of a melt is kept low and formation of boronnitride is inhibited. Accordingly, generation of dislocation due toboron nitride is prevented and a single crystal with a large diameterand high gettering ability can be produced at high productivity.

It is preferable that a single crystal with a diameter of 200 mm or moreis grown as the single crystal.

When a single crystal with a large diameter of 200 mm or more is grown,a large crucible is used. In this case, a distance between the crucibleand the crystal is large, and thus the crucible is heated to a hightemperature to grow a single crystal with keeping molten state of a meltin the crucible. Therefore, boron nitride comes to be easily generated.However, even in the case of growing such a single crystal with a largediameter, formation of boron nitride is inhibited by performing growthwith controlling the highest temperature of a crucible to be 1600° C. orless, and thus a single crystal with a large diameter can be produced athigh productivity.

As mentioned above, according to the present invention, in the case ofgrowing a single crystal of which resistivity is adjusted by doping withboron by Czochralski method, the highest temperature of a crucible iscontrolled to be 1600° C. or less to grow the single crystal. Bycontrolling the temperature of the crucible to be 1600° C. or less, atemperature of a material melt in the crucible is kept low, and thusformation of boron nitride can be inhibited. Accordingly, frequency ofgeneration of dislocation in a single crystal due to boron nitride isconsiderably reduced. Thus, a P-type single crystal having a highgettering ability can be produced at high productivity. As a result,decrease of production cost can be achieved.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of an apparatus forproducing a single crystal that can be used in the present invention.

FIG. 2 is a schematic view showing another example of an apparatus forproducing a single crystal that can be used in the present invention.

FIG. 3 is a schematic view showing a further example of an apparatus forproducing a single crystal that can be used in the present invention.

FIG. 4 is a schematic view showing an example of a conventionalapparatus for producing a single crystal.

FIG. 5 is a graph in which productivity of examples and a comparativeexample are compared.

FIG. 6 is a graph showing the relation between the highest temperatureof a crucible and ratio of productivity.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be explained in more detail.

The present inventors made investigation into various situations ofgenerating dislocation by using various analysis methods (IR, X-raydiffraction, Raman spectroscopy, fluorescent X-ray and the like).Consequently, one of causes of generating dislocation of a boron-dopedsingle crystal with low resistivity could be identified as boron nitride(BN) formed as a result of reaction of nitrogen and boron. Boron nitrideis generated at a temperature of approximately 1500° C. or more.However, once boron nitride is generated, it doesn't dissolves but thatit is under pressure at 3000° C., and thus it becomes the cause ofgenerating dislocation. Namely, it is considered that, when such a boronnitride adheres to a single crystal during growth, dislocation isgenerated in the growing single crystal.

In particular, in growth of a boron-doped single crystal with lowresistivity, concentration of boron in a melt is higher than that ingrowth of a single crystal with normal resistivity. Therefore, it isconsidered that boron nitride is easily generated not only in the caseof further doping with nitrogen, but also in the case that boron reactswith nitride included in a quartz crucible or generated due to nitrogenin an atmosphere, or nitrogen slightly incorporated in an apparatus forgrowing a crystal through mechanical leak.

Moreover, the present inventors considered that, when boron nitride isgenerated in a melt and dislocation is generated, it is very unlikelythat the boron nitride is dissolved by remelting, as in a conventionalway, the crystal in which dislocation was generated, and it is verylikely that boron nitride floats in a melt and adheres again to agrowing crystal while the crystal is grown again.

Then, the present inventors considered that melting point of silicon wasapproximately 1420° C., softening point of a quartz crucible wasapproximately 1750° C., and although the temperatures of the siliconmelt and the crucible were kept between these temperatures duringgrowth, it was important to keep temperatures of a crucible and a meltas low as possible in order to inhibit generation of boron nitride. Thatis, because generation temperature of boron nitride is approximately1500° C. or more, by controlling the highest temperature of a crucibleto be less than 1500° C., temperature of a silicon melt in the crucibleis also low and generation of boron nitride can be inhibited.

However, the larger a diameter of crystal becomes, the larger a size ofcrucible to be used becomes. Since a heater power also becomes larger inorder to grow the crystal with keeping molten state all over the melt, atemperature of the crucible increases. Therefore, there are some casesthat it is difficult to grow a single crystal with controlling thehighest temperature of a crucible to be less than 1500° C.

Then, the present inventors performed investigations and studies.Consequently, it has been found that, in the case of growing a singlecrystal doped with boron, if the single crystal is grown withcontrolling the highest temperature of a crucible to be 1600° C. orless, reaction of boron and nitrogen is inhibited, frequency ofgenerating dislocation due to boron nitride is considerably decreased,and as a result, productivity can be improved and cost can be lowered.Thus, the present invention has been accomplished.

Hereinafter, according to the present invention, the cases of producinga silicon single crystal doped with boron as dopant at highconcentration, and a silicon single crystal doped with boron andnitrogen as dopant will be explained by referring to the appendeddrawings.

FIG. 1 is a schematic view showing an example of an apparatus forproducing a single crystal (a pulling apparatus) that can be used in thepresent invention. The apparatus 20 for producing a single crystal has amain chamber 1 equipped with a crucible 5 for containing material melt 4therein and a heater 7, and a pulling chamber 2 for accommodating andtaking out a single crystal ingot 3 pulled from the material melt 4.

The crucible 5 is composed of an inner quartz crucible 5 a and an outergraphite crucible 5 b, and it is disposed on a pedestal 15 and can bemoved upwardly or downwardly with being rotated via a rotating shaft 16by crucible control means (not shown) disposed below.

A heater 7 is provided so as to surround the crucible 5, and a heatinsulating member 8 is further provided outside the heater 7.

A gas flow-guide cylinder (an auxiliary cooling cylinder) 11 a isprovided from between the main chamber 1 and the pulling chamber 2 to amelt surface, and further a heat shielding member 12 is provided at thetip of the gas flow-guide cylinder 11 a. Moreover, above the mainchamber 1, an optical device (not shown) for measuring and monitoring adiameter and a condition of the growing single crystal ingot 3 isprovided.

The pulling chamber 2 is constructed to be openable so that an alreadygrown single crystal can be taken out, and above the pulling chamber 2,crystal pulling means (not shown) for pulling the single crystal 3 withbeing rotated via a wire (or a shaft) 13 is provided.

In order to produce a silicon single crystal doped with boron at highconcentration using such an apparatus 20, in addition to polycrystallinematerial, boron dopant like metal boron element for example, iscontained into the crucible 5, or in order to produce a silicon singlecrystal doped with boron and nitrogen, nitrogen dopant like siliconnitride as well as boron dopant is contained therein.

Amount of the boron dopant to be added may be decided according todesired resistivity of a silicon single crystal because the amount isreflected by boron concentration in a single crystal to be grown, thatis, resistivity. Generally, in the case that a single crystal with a lowresistivity of 0.1 Ω cm or less is grown, boron concentration in a meltbecomes high and boron nitride comes to be easily generated even whennot doping with nitrogen intentionally.

When growing a single crystal with a resistivity less than 0.001 Ω cm,concentration of boron in a melt becomes extremely high and exceeds thesolid solubility limit of boron to silicon, and thus it becomesdifficult to be crystallized as a single crystal. Accordingly, it ispreferable that boron dopant is doped so as to become the concentrationof boron where resistivity of a single crystal to be grown is from 0.001Ω cm to 0.1 Ω cm.

On the other hand, because amount of nitrogen dopant is also reflectedby concentration of nitrogen in a single crystal to be grown, amount ofthe dopant may be decided in accordance with desired concentration ofnitrogen of a silicon single crystal. When concentration of nitrogen ina single crystal is too low, effects on BMD and Grown-in defects aren'tsufficiently obtained. Thus it is preferable that concentration ofnitrogen is 1×10¹⁰/cm³ or more, which causes sufficient heterogeneousnucleation.

However, when concentration of nitrogen in a melt exceeds the solidsolubility limit to silicon, it becomes difficult to be crystallized asa single crystal. Therefore, it is preferable that nitrogen dopant isdoped so that the concentration of nitrogen in a single crystal to begrown is 5×10¹⁵/cm³ or less.

When nitrogen is intentionally doped as mentioned above, boron nitridecomes to be easily generated almost irrespective of concentration ofboron, for example, even in the case of low concentration of boron whereresistivity becomes approximately 1000 Ω cm.

After raw material and dopant are charged into the crucible 5 and areheated and melted by the heater 7, a wire 13 is gently reeled outdownwardly from above, and a seed crystal 14, which has a form ofcircular cylinder or rectangular column and is suspended by a holder 6attached at the end of the wire 13, is contacted with a melt surface(immersed in the melt). Next, after necking is performed in which theseed crystal 14 is pulled carefully upwardly with being rotated and adiameter is gradually thinned, the diameter of the neck portion isenlarged by controlling the pulling rate, temperature and the like totransfer to growth of cone portion of the single crystal ingot 3.Moreover, after a diameter of the cone portion is enlarged to aprescribed diameter, it is transferred to growth of a straight body witha desired diameter by controlling the pulling rate and temperature ofthe melt again.

Because the material melt 4 is decreased and the melt surface is loweredalong with the growth of the single crystal 3, it is controlled that thecrucible 5 is elevated so as to maintain the level of the melt surfaceto be constant, thereby the growing single crystal ingot 3 keeps aprescribed diameter.

Further, during the operation, an argon gas is introduced into thechambers 1 and 2 from a gas inlet 10, and then discharged from a gasoutlet 9, thereby the operation is performed under argon atmosphere.

When a single crystal is grown as mentioned above, there is a case thatdislocation is generated in the growing single crystal. When such adislocation is generated, an operation in which the grown single crystalis melted again and a single crystal is grown again from the samematerial melt is conventionally repeated. However, according to theinvestigations of the present inventors, it has been found that, when aP-type single crystal with a low resistivity is particularly grown by CZmethod, boron nitride is easily generated in a melt even in the case ofnot doping with nitrogen intentionally, and adhesion of the boronnitride to the crystal causes generation of dislocation. Since oncegenerated boron nitride (BN) is difficult to dissolve, it is very likelyto generate dislocation again even if remelting and regrowing isrepeated again and again.

Then, in the present invention, when a single crystal doped with boronis grown as mentioned above, in order to inhibit formation of boronnitride, the single crystal is grown with the highest temperature of acrucible being controlled to be 1600° C. or less. As mentioned above,boron nitride is generated when a temperature of a material melt isapproximately 1500° C. or more. However, when the highest temperature ofa crucible is controlled to be 1600° C. or less to perform growth, atemperature of a material melt is kept low, and thus generation of boronnitride can be effectively inhibited.

However, if the highest temperature of a crucible is lowered to aroundthe melting point of silicon (1420° C.), there is a possibility that itbecomes difficult to grow a single crystal with maintaining molten stateof entire material. For this reason, although it depends on a size of acrucible to be used and the like, it is preferable that the highesttemperature of the crucible is controlled to be from 1450° C. to 1600°C., in particular, from 1480° C. to 1550° C.

As for control of a temperature of a crucible, for example, the highesttemperature can be controlled to be 1600° C. or less by adjusting afurnace structure (hot zone structure) such as position of a heatshielding member, height of a heat insulating member and so on.

In the pulling apparatus 20 shown in FIG. 1, the distance from a meltsurface to the auxiliary cooling cylinder (gas flow-guide cylinder) 11 aextends 2.5 times as long. as that of the apparatus 30 shown in FIG. 4.Generally, when a single crystal is grown, heater power is set so that atemperature in the vicinity of solid-liquid interface between a meltsurface and a single crystal becomes a desired value. However, when aheat insulating member 8 around the heater 7 is relatively low asapparatuses shown in FIGS. 1 and 4, radiation becomes larger, and thecrucible 5 and the melt 4 are overheated by the heater 7. However, whenthe distance between the auxiliary cooling cylinder 11 a (heat shieldingmember 12) and the melt surface is enlarged as the apparatus 20 shown inFIG. 1, cooling effect on the crucible 5 and the melt 4 is increased,and thus the temperature of the crucible 5 (the quartz crucible 5 a) canbe maintained to be 1600° C. or less.

Furthermore, in the apparatus 20 a shown in FIG. 2, the heat insulatingmember 8 a surrounding the heater 7 is higher than that of the apparatus30 shown in FIG. 4, and thus radiation becomes smaller. In addition, theapparatus 20 b shown in FIG. 3 adopts a heat shielding member 12 a witha thin thickness as well as the auxiliary cooling cylinder 11 a shown inFIG. 1 and the heat insulating member 8 a shown in FIG. 2. Becauseoverheat of the crucible 5 by the heater 7 is prevented and coolingeffect is increased also in these apparatuses 20 a and 20 b, thetemperature of the crucible 5 (the quartz crucible 5 a) can be keptlower, that is, at 1600° C. or less.

When a single crystal is practically grown using these apparatuses 20,20 a and 20 b, for example, various conditions (heater power, distancebetween the auxiliary cooling cylinder and the melt surface, length ofthe heat insulating member, form of the heat shielding member, and thelike) may be controlled according to calculation by computer simulationbeforehand so that the highest temperature of the crucible is 1600° C.or less. Alternatively, it is possible that the temperature of thecrucible is really measured by using a thermocouple and the like, and afurnace structure is controlled so that the highest temperature of thecrucible is 1600° C. or less.

In addition, an apparatus that controls the highest temperature of acrucible to be 1600° C. or less is not limited to the apparatuses 20, 20a and 20 b as shown in FIGS. 1-3. It is also possible to use, forexample, as disclosed in Japanese Patent Laid-open (Kokai) No. 9-227276,an pulling apparatus that can control the highest temperature of acrucible to be 1600° C. or less by setting an auxiliary heater or thelike above the crucible to prevent deterioration of the crucible.

Furthermore, a size of a single crystal grown according to the presentinvention is not particularly limited. However, when a silicon singlecrystal with a large diameter of 200 mm or more, particularly 300 mm isgrown, it is often the case that the growth is performed by MCZ methodby using an apparatus equipped with a device for applying a magneticfield outside of the main chamber 1. At this time, if a magnetic fieldis applied with the central magnetic field intensity of 300 gauss ormore, an effect of suppressing a convection of a melt is increased. Thusa temperature of the melt becomes high and boron nitride is easilygenerated. However, if the growth is performed with controlling thehighest temperature of a crucible to be 1600° C. or less, formation ofboron nitride can be inhibited. Accordingly, a single crystal with largediameter and high gettering ability can be produced by MCZ method athigh productivity.

Then a wafer with low resistivity, which is obtained by processing thesilicon single crystal produced as above via the steps of slicing,chamfering, lapping, etching, polishing, and the like, has an extremelyexcellent gettering ability because its resistivity is low, and thus itcan be advantageously used as a substrate for an epitaxial wafer.

Hereinafter, the present invention will be explained in reference toexamples and a comparative example.

EXAMPLE 1

By using the apparatus 20 for producing a single crystal (a diameter ofa crucible : 800 mm) of which scheme is shown in FIG. 1, a P-type(boron-doped) silicon single crystal with a diameter of 12 inches (300mm) was grown by Czochralski method (CZ method).

In the step of melting, 320 kg of polycrystalline silicon material wascharged into the crucible, at the same time metal boron element forcontrolling resistivity was added. The amount of the boron was adjustedso that the resistivity of the single crystal to be grown was in therange of 0.005-0.01 Ω cm.

Moreover, the distance between an auxiliary cooling cylinder and a meltsurface was set to be 75 mm.

In the step of growing a crystal, horizontal magnetic field in whichcentral magnetic field intensity was 3500 G was applied and a crystal inwhich a length of the straight body was approximately 120 cm was grown.

The highest temperature of the crucible calculated by FEMAG (the globalheat transfer analysis software: F. Dupret, P. Nicodeme, Y. Ryckmans, P.Wouters, and M. J. Crochet, Int. J. Heat Mass Transfer, 33, 1849 (1990))under above conditions was 1543° C.

In the case that dislocation was generated in a crystal during growth,the crystal was melted again and growth is performed again, and until acrystal that can be used as a product was obtained, remelting andregrowing were repeated.

The number of generation of dislocation in this furnace structure untila single crystal as a product was obtained was approximately ⅕ of thatin the following Comparative example.

Comparative Example

A crystal was grown under the same conditions as Example 1, except thatthe furnace structure of which scheme was shown in FIG. 4 was used, andthe distance between the auxiliary cooling cylinder and the melt surfacewas set to be 30 mm. At this time, the highest temperature of thecrucible calculated by FEMAG was 1627° C.

In this apparatus, generation of dislocation frequently happened as inthe past until a crystal as a product was obtained.

EXAMPLE 2

A single crystal was grown under the same conditions as Example 1,except that the apparatus of which scheme was shown in FIG. 2 was used,the distance between the auxiliary cooling cylinder and the melt surfacewas set to be 30 mm, and the heat insulating member was higher by 20 cm.In this apparatus, the heat insulating member was longer and the highesttemperature of the crucible calculated by FEMAG was 1597° C.

The number of generation of dislocation in this apparatus until a singlecrystal as a product was obtained was approximately ½ of that in theabove Comparative example.

EXAMPLE 3

A single crystal was grown under the same conditions as Example 1,except that the apparatus of which scheme was shown in FIG. 3 was used,a thickness of the heat shielding member was thin, and the heatinsulating member was higher by 20 cm. In this apparatus, the highesttemperature of the crucible calculated by FEMAG was 1563° C.

The number of generation of dislocation in this apparatus until a singlecrystal was obtained was approximately ⅕ of that in Comparative example.It was slightly more than Example 1.

Comparison of Productivity

Productivities in above Examples and Comparative example are compared inFIG. 5. Furthermore, productivity ratio is plotted to the highesttemperature of the crucible in FIG. 6.

As shown in FIG. 5, productivity in Example 1 was 1.73 times as large asthat in Comparative example, Example 2 was 1.53 times and Example 3 was1.61 times. All of Examples were good result.

Moreover, as seen in FIG. 6, productivity was clearly lower in the casethat the highest temperature of the crucible is close to 1630° C.(Comparative example), than the case that the temperature is controlledat 1600° C. or less (Examples 1-3).

The present invention is not limited to the embodiments described above.The above-described embodiments are mere examples, and those havingsubstantially the same structure as technical ideas described in theappended claims and providing the similar functions and advantages areincluded in the scope of the present invention.

1. A method of producing a single crystal according to Czochralskimethod comprising the steps of, charging polycrystalline material into acrucible, heating and melting the polycrystalline material by a heaterdisposed so as to surround the crucible, immersing a seed crystal intothe material melt and then pulling the seed crystal to grow a singlecrystal, wherein in the case of growing a single crystal of whichresistivity is controlled by doping with boron, the highest temperatureof the crucible is controlled to be 1600° C. or less to grow the singlecrystal.
 2. The method of producing a single crystal according to claim1, wherein the single crystal doped with boron is grown so that theresistivity of the single crystal to be grown is 0.1 Ω cm or less. 3.The method of producing a single crystal according to claim 2, whereinthe single crystal doped with boron is grown so that the resistivity ofthe single crystal to be grown is 0.001 Ω cm or more.
 4. The method ofproducing a single crystal according to claim 1, wherein the singlecrystal doped with nitrogen is grown so that concentration of nitrogenin the single crystal to be grown is from 1×10¹⁰/cm³ to 5×10¹⁵/cm³. 5.The method of producing a single crystal according to claim 2, wherein asilicon single crystal is grown as the single crystal.
 6. The method ofproducing a single crystal according to claim 3, wherein in the case ofgrowing the single crystal, a magnetic field of at least 300 gauss ormore is applied to the material melt to grow the single crystal.
 7. Themethod of producing a single crystal according to claim 1, wherein asingle crystal with a diameter of 200 mm or more is grown as the singlecrystal.
 8. The method of producing a single crystal according to claim2, wherein a silicon single crystal is grown as the single crystal. 9.The method of producing a single crystal according to claim 3, wherein asilicon single crystal is grown as the single crystal.
 10. The method ofproducing a single crystal according to claim 4, wherein a siliconsingle crystal is grown as the single crystal.
 11. The method ofproducing a single crystal according to claim 5, wherein a siliconsingle crystal is grown as the single crystal.
 12. The method ofproducing a single crystal according to claim 6, wherein a siliconsingle crystal is grown as the single crystal.
 13. The method ofproducing a single crystal according claims 7, wherein in the case ofgrowing the single crystal, a magnetic field of at least 300 gauss ormore is applied to the material melt to grow the single crystal.
 14. Themethod of producing a single crystal according claims 8, wherein in thecase of growing the single crystal, a magnetic field of at least 300gauss or more is applied to the material melt to grow the singlecrystal.
 15. The method of producing a single crystal according claims9, wherein in the case of growing the single crystal, a magnetic fieldof at least 300 gauss or more is applied to the material melt to growthe single crystal.
 16. The method of producing a single crystalaccording claims 10, wherein in the case of growing the single crystal,a magnetic field of at least 300 gauss or more is applied to thematerial melt to grow the single crystal.
 17. The method of producing asingle crystal according claims 11, wherein in the case of growing thesingle crystal, a magnetic field of at least 300 gauss or more isapplied to the material melt to grow the single crystal.
 18. The methodof producing a single crystal according claims 12, wherein in the caseof growing the single crystal, a magnetic field of at least 300 gauss ormore is applied to the material melt to grow the single crystal.
 19. Themethod of producing a single crystal according to claim 17, wherein asingle crystal with a diameter of 200 mm or more is grown as the singlecrystal.
 20. The method of producing a single crystal according to claim18, wherein a single crystal with a diameter of 200 mm or more is grownas the single crystal.